IZÚCAR DE MATAMOROS, Mexico — Jeffrey Isidoro sat near the door of his fifth-grade classroom here in central Mexico, staring outside through designer glasses that, like his Nike sneakers and Nike backpack, signaled a life lived almost entirely in the United States. His parents are at home in Mexico. Jeffrey is lost.

When his teacher asked in Spanish how dolphins communicate, a boy next to him reached over to underline the right answer. When it was Jeffrey’s turn to read, his classmates laughed and shouted “en inglés, en inglés” — causing Jeffrey to blush.

“Houston is home,” Jeffrey said during recess, in English. “The houses and stuff here, it’s all a little strange. I feel, like, uncomfortable.”

Never before has Mexico seen so many American Jeffreys, Jennifers and Aidens in its classrooms. The wave of deportations in the past few years, along with tougher state laws and persistent unemployment, have all created a mass exodus of Mexican parents who are leaving with their American sons and daughters.

In all, 1.4 million Mexicans — including about 300,000 children born in the United States — moved to Mexico between 2005 and 2010, according to Mexican census figures. That is roughly double the rate of southbound migration from 1995 to 2000, and new government data published this month suggest that the flow is not diminishing. The result is an entire generation of children who blur the line between Mexican and American.

“It’s really a new phenomenon,” said Víctor Zúñiga, a sociologist at the University of Monterrey, in Nuevo León State, which borders Texas. “It’s the first time in the relationship between Mexico and the United States that we have a generation of young people sharing both societies during the early years of their lives.”

Critics of immigration have mostly welcomed the mass departure, but demographers and educators worry that far too many American children are being sent to schools in Mexico that are not equipped to integrate them. And because research shows that most of these children plan to return to the United States, some argue that what is Mexico’s challenge today will be an American problem tomorrow, with a new class of emerging immigrants: young adults with limited skills, troubled childhoods and the full rights of American citizenship.

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Jeffrey Isidoro, 10, misses Houston and has had a hard time making friends at school in Izúcar de Matamoros in central Mexico.Credit
Shaul Schwarz for The New York Times

“These kinds of changes are really traumatic for kids,” said Marta Tienda, a sociologist at Princeton who was born in Texas to Mexican migrant laborers. “It’s going to stick with them.”

Jeffrey’s situation is increasingly common. His father, Tomás Isidoro, 39, a carpenter, was one of the 46,486 immigrants deported in the first half of 2011 who said they had American children, according to a report by Immigration and Customs Enforcement to Congress. That is eight times the half-year average for such removals from 1998 to 2007.

Mr. Isidoro, wearing a Dallas Cowboys hat in his parents’ kitchen, said he was still angry that his 25 years of work in the United States meant nothing; that being caught with a broken taillight on his vehicle and without immigration papers meant more than having two American sons — Jeffrey, 10, and his brother, Tommy Jefferson, 2, who was named after the family’s favorite president.

As for President Obama, Mr. Isidoro uttered an expletive. “There are all these drug addicts, drug dealers, people who do nothing in the United States, and you’re going to kick people like me out,” he said. “Why?”

White House officials have said that under a new policy focused on criminals, fewer parents of American children are being deported for minor offenses. On Friday, the Obama administration also announced that hundreds of thousands of illegal immigrants who came to United States as children would be allowed to stay without fear of deportation. The policy, however, does not grant legal status, and because nearly half of the country’s 10.2 million illegal immigrant adults have children, experts say that inevitably more families will be divided — especially if deportations over all hold steady around 400,000 a year.

But for Jeffrey, the impact of his father’s removal in June last year was immediate. His grades dipped. His mother, Leivi Rodríguez, 32, worried that he had become more distant, from both his friends and his studies. Almost every day, Jeffrey told her he wanted to see his father.

So six months after her husband’s deportation, she sent Jeffrey to live with his father in Mexico, and she followed with Tommy a few months later. It was December when he arrived here in a hill town south of Mexico City, surrounded by fields of swaying sugar cane. On Jeffrey’s first night, he noticed something strange in his bed. “Dad, what’s that?” he asked.

“A scorpion,” his father said.

School here presented new challenges, as well. Jeffrey went hungry at first because neither he nor his father realized that without a cafeteria, students relied on their parents to bring them food at recess.

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"There are all these drug addicts, drug dealers, people who do nothing in the United States, and you're going to kick me out." — TOMÁS ISIDORO, Jeffrey's father, deported after living 25 years in the United StatesCredit
Shaul Schwarz for The New York Times

In class, Jeffrey’s level of confusion rises and falls. His teacher said she struggled to keep him from daydreaming. “His body is here, but his mind — who knows where it is,” she said.

Houston — that is where Jeffrey’s thoughts typically drift. There, he had friends, McDonald’s, the zoo. It is where he lingered at the library at Gleason Elementary to catch up on his favorite series of books, “Diary of a Wimpy Kid.” There, his school had a playground; here, there is just a concrete slab. There, computers were common; here, there are none.

“It was just better,” Jeffrey said.

The educational disparities between Mexico and the United States are not always so stark. At the elementary level, some of Mexico’s schools are on par with, or even stronger than, the overcrowded, underfinanced American schools that serve many immigrant children, education experts say.

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But Mexican schools lag when it comes to secondary education. In many areas of Mexico, especially places where the tradition of migration is not as well established, Mexico’s educational bureaucracy can make life difficult for new arrivals like Jeffrey. It is not uncommon for American students to be barred from enrollment for a year or more because they lack proper documents.

“The established rules for registration don’t need to be so severe,” said Armando Reynoso Carrillo, a state legislator from Malinalco, a rural area in Mexico State where dozens of American children have arrived in recent years.

The problems extend beyond registration. Mexicans have a long history of greeting returnees with skepticism — for abandoning Mexico, or because they resent the United States, or view those who moved there as materialistic, culturally out of touch and arrogant. The prejudice often extends to their children.

Graciela Treviño González said that when she returned to Malinalco three years ago, after more than a decade in California, she could not get her American son onto a soccer team because the coaches refused to accept him without Mexican identification. “He felt rejected by everyone,” she said. “The kids called him ‘leche,’ ‘gringo’ — it was awful.” Leche means milk and gringo can range from a neutral reference to a foreigner to a slur.

Here in the central state of Puebla, Mexican children are especially likely to see transnational students as different, according to surveys by Mr. Zúñiga, the sociologist. Some have come to Mexico because of deportations. Others arrived because relatives were sick or without work.

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A family photo of Jeffrey in front of their home in Virginia, where they lived before moving to Texas and then Mexico.Credit
Shaul Schwarz for The New York Times

But regardless of the cause, Mexican students tend to see their American-educated colleagues as strangers. Jeffrey’s experience is typical: He is friendly and quick to open up in English, but quieter at school, where Spanish is the only language one hears.

At one point this spring, as Jeffrey sat at the edge of the playground, a larger boy approached from behind and asked if he was from Florida or Houston. When Jeffrey pulled away because the boy had leaned into him, the bigger boy seemed surprised. “Are you mad?” he asked.

Later, other boys tested Jeffrey on his English, asking him in Spanish to translate various body parts.

“How do you say foot?” one asked. “Finger?”

“Eye?”

Jeffrey provided one-word answers without enthusiasm. At home, a three-room concrete box with furniture hauled from Houston, he said that many of the children called him Four Eyes. He said he was starting to feel more comfortable academically and socially, but even in a school with 11 other children born or educated in the United States (out of 296) he is still a foreigner. Sometimes, he confuses the Mexican pledge of allegiance with the American version.

Ms. Tienda, at Princeton, said children of Jeffrey’s age were more likely to struggle with such a difficult transition. “This is the age where they start to be aware of each other’s differences,” she said. “They’re preadolescents and their identity is being crystallized.”

She added that how these students fared over the long term will probably vary widely. Some will make the transition easily while others will suffer setback after setback. It will depend on their language skills, school and family dynamics.

Jeffrey, like many other children whose parents have moved them to a country they do not know, seems to be teetering between catching up to his classmates and falling further behind. His parents are struggling to find work and keep their marriage together. Jeffrey, in quieter moments, said he was just trying to endure until he could go home.

“I dream, like, I’m sleeping in the United States,” he said. “But when I wake up, I’m in Mexico.”

Shaul Schwarz contributed reporting.

A version of this article appears in print on June 19, 2012, on Page A1 of the New York edition with the headline: American Children, Now Struggling to Adjust to Life in Mexico. Order Reprints|Today's Paper|Subscribe